The present invention relates to an improved process for the preparation of novel antidiabetic compounds having the formula (1). 
where R1 represents hydrogen or lower alkyl group, and X represents hydrogen or halogen
U.S. patent application Ser. No. 09/012,585, now U.S. Pat. No. 6,054,453, describes a process for the preparation of a novel antidiabetic compound having the formula (1). The process described therein comprises converting aldehyde of formula (2) where X is as defined above to a compound of formula (3) where all symbols are as defined above and R2 represents lower alkyl group, reducing the compound of formula (3) to produce a compound of formula (4), hydrolysing the compound of formula (4) to obtain an acid of formula (5), converting the acid of formula (5) to an amide of the formula (6) and hydrolysing the amide to produce the compound of formula (1), where X and R1 are as defined above. The process is shown in the scheme-1 given below 
The main objective of the present invention is therefore to provide a convergent synthesis of the compounds of the formula (1).
Another objective of the present invention is to provide a convergent and stereoselective synthesis of the compounds of the formula (1) and a commercial viable process.
Another objective of the present invention is to provide a process for the preparation of the compounds of the formula (1) by preparing chiral amine addition salts followed by hydrolysis to afford the uni-isomer of an intermediate which can later be converted into the required isomers having the formula (1). In the event of a small amount of racemization, if any, during the course of converting the intermediate to the final compounds of the formula (1), resolution can easily be done by employing chiral amines without losing much of the compounds of the formula (1).
Accordingly, the present invention provides a process for the preparation of compounds of the formula (1) where R1 represents hydrogen atom or lower alkyl group such as C1-C6 group preferably methyl, ethyl, propyl and the like, X represents hydrogen atom or halogen atom such as chlorine, bromine or iodine which comprises:
(i) benzylamino p-hydroxybenzldehyde of the formula (7) by conventional methods to yield a compound of the formula (8),
(ii) reacting the compound of the formula (8) with alkyl haloacetates in the presence of a base at a temperature in the range of xe2x88x9210xc2x0 C. to 60xc2x0 C. (Darzen""s condensation) to yield the glycedic ester of the formula (9) where R represents lower alkyl group,
(iii) opening up the epoxide group of the glycedic ester of the compound of the formula (9) by conventional methods to yield a compound of the formula (10) where R is as defined above,
(iv) hydrolyzing the compound of the formula (10) by conventional methods followed by the resolution of the resultant compound to yield (S)-hydroxy compound of the formula (11),
(v) converting the compound of the formula (11) to the corresponding alkylated compound of the formula (12) where R1 represents hydrogen or lower alkyl, R2 represents lower alkyl group in one pot reaction by treating it with an alkylating agent in the presence of base,
(vi) debenzylating the compound of the formula (12) by conventional methods to produce the compound of the formula (13) where R1 and R2 are as defined above, if desired,
(vii) converting the compound of the formula (13) to a compound of formula (14) where X represents halogen atom and all other symbols are as defined above by conventional methods,
(viii) reacting either the compound of the formula (13) or the compound of the formula (14) with phenoxazinyl mesylate of the formula (15) to give the ester of the formula (16) where X represents hydrogen or halogen atom, and R1 and R2 are as defined above,
(ix) hydrolysing the compound of the formula (16) by conventional methods to yield the compound of the formula (1) defined above, and if desired,
(x) chemically resolving the compound of formula (1) by employing chiral amines, in case there is any racemization during the course of converting the (S)-hydroxy compound of the formula (11) to the final compound of formula (1).
The process explained above is shown in scheme-2 below: 
Benzyl protection of p-hydroxybenzaldehyde having the formula (7) affords the protected aldehyde of the formula (8). Reaction of the compound of the formula (8) with alkylhaloacetates such as methyl chloroacetate, methylbromoacetate, ethylchloroacetate, ethylbromoacetate, and the like in the presence of a base such as sodium methoxide, sodium ethoxide, sodium carbonate, potassium carbonate, potassium sec. Butoxide, t-BuOK and the like gives the glycedic ester of the formula (9) where R represents lower alkyl group such as C1-C6 alkyl preferably methyl, ethyl and the like. The glycedic ester of the formula (9) is opened up with reagents such as Raney. Ni, H2/Pdxe2x80x94C, borane reagents, and the like to give the racemic hydroxy ester having the formula (10). Hydrolysis of the ester of the formula (10) followed by its resolution using chiral amines such as R(+)xcex1-methylbenzylamine, S(+)-phenylglycinol, cinchonidine, ephedrine, n-octylglucosamine and the like gives the optically active hydroxy acid having the formula (11), which on alkylation using alkylating agents such as diethylsuphate, ethyliodide, methyliodide, dimethylsuphate and the like, in the presence of a base such as NaH, NaOH, KOH, t-BuOK, K2CO3, NaHCO3, and the like, affords the compound of the formula (12) where R1 represents hydrogen or lower alkyl group such as C1-C6 group preferably methyl, ethyl, propyl and the like, R2 represents lower alkyl group such as C1-C6 group preferably methyl, ethyl, propyl and the like. The compound of the formula (12) upon debenzylation using reagents such as H2/Pdxe2x80x94C, HCl/AcOH, and the like in the presence of solvents such as THF, ethylacetate, 1,4-dioxane, AcOH and the like gives the substituted phenol of the formula (13). The compound of the formula (13) is converted to a compound of formula (14) using suitable halogenating agents such as ICl/HCl, I2/KI, Cl2/H+, Br2/AcOH and the like. The optically active compound of the formula (13) or the compound of the formula (14) reacts with the phenoxazinyl mesylate having the formula (15) to give the ester of the formula (16) which on hydrolysis employing conventional methods yields the required compound of the formula (1) in an optically pure form. However, in the event of a small amount of racemization, if any, during the course of converting the intermediate of the formula (11) to the final compound of the formula (1), resolution can easily be done employing chiral amines such as those described above without losing much of the compound of the formula (1).
The present invention also provides another improved process for the preparation of compounds of the formula (1) described above which comprises:
(i) benzylamino p-hydroxybenzaldehyde of the formula (7) by conventional methods to yield a compound of the formula (8),
(ii) reacting the compound of the formula (8) with alkyl haloacetates in the presence of a base at a temperature in the range of xe2x88x9210xc2x0 C. to 60xc2x0 C. (Darzen""s condensation) to yield the glycedic ester of the formula (9) where R represents lower alkyl group,
(iii) opening up the epoxide group of the glycedic ester of the compound of the formula (9) by conventional methods to yield a compound of the formula (10) where R has the meaning given above,
(iv) alkylating the compound of the formula (10) using alkylating agent in the presence of a base to obtain a compound of the formula (12a) where R1 represents hydrogen or lower alkyl, R2 represents lower alkyl group,
(v) debenzylating the compound of the formula (12a) by conventional methods to produce the compound of the formula (13a) where R1 and R2 are as defined above, if desired,
(vi) converting the compound of the formula (13a) to a compound of formula (14a) where X represents halogen atom R1 and R2 are as defined above by conventional methods,
(vii) reacting either the compound of the formula (13a) or the compound of formula (14a) with phenoxazinyl mesylate of the formula (15) to give the ester of the formula (4) where X represents hydrogen or halogen atom, R1 and R2 are as defined above,
(viii) hydrolysing the compound of the formula (4) by conventional methods to yield the racemic compound of the formula (5) where X represents hydrogen or halogen atom, R1 and R2 are as defined above, and
(ix) chemically resolving the compound of formula (5) by employing chiral amines, to the final compound of formula (1) optionally through an intermediate amide of the formula (6) where X represents hydrogen or halogen atom and R1 are as defined above.
The process explained above is shown in scheme-3 below: 
Benzyl protection of p-hydroxybenzaldehyde having the formula (7) affords the protected aldehyde of the formula (8). Reaction of the compound of the formula (8) with alkylhaloacetates such as methylchloroacetate, methylbromoacetate, ethylchloroacetate, ethylbromoacetate, and the like in the presence of a base such as sodium methoxide, sodium ethoxide, sodium carbonate, potassium carbonate, potassium sec. Butoxide, t-BuOK and the like gives the glycedic ester of the formula (9) where R represents lower alkyl group such as C1-C6 group, preferably methyl, ethyl, and the like. The glycedic ester of the formula (9) is opened up with reagents such as Raney. Ni, H2/Pdxe2x80x94C, borane reagents, and the like to give the racemic hydroxy ester having the formula (10), which on alkylation using alkylating agents such as diethylsuphate, ethyliodide, methyliodide, dimethylsuphate and the like, in the presence of a base such as NaH, NaOH, KOH, t-BuOK, K2CO3, NaHCO3 and the like affords the compound of the formula (12a) where R1 represents hydrogen or lower alkyl group such as C1-C6 group preferably methyl, ethyl, propyl and the like, R2 represents lower alkyl group such as C1-C6 group, preferably methyl, ethyl, propyl and the like. The ethoxy ester of the formula (12a) upon debenzylation using reagents such as H2/Pdxe2x80x94C, HCl/AcOH, and the like in the presence of solvents such as THF, ethyl acetate, 1,4-dioxane, AcOH and the like gives the substituted phenol of the formula (13a). The compound of the formula (13a) is converted to a compound of formula (14a) using suitable halogenating agents such as ICl/HCl, I2/KI, Cl2/H+, Br2/AcOH and the like. The compound of the formula (13a) or the compound of formula (14a) reacts with the phenoxazinyl mesylate having the formula (15) to give the ester of the formula (4) which on hydrolysis employing conventional methods gives racemic acid of the formula (5). The racemic acid on resolution using chiral amines such as R(+)xcex1-methylbenzylamine, S(+)-phenylglycinol, cinchonidine, ephedrine, n-octylglucosamine and the like, yields the required compound of the formula (1) in an optically pure form optionally through an intermediate amide of the formula (6).
The present invention also provides yet another improved process for the preparation of compound of the formula (1) described above which comprises:
(i) reacting p-hydroxybenzaldehyde of the formula (7) with hydantoin of the formula (17) by conventional methods to yield a compound of the formula (18),
(ii) hydrolysing the compound of the formula (18) by conventional methods to yield a compound of the formula (19),
(iii) reducing the compound of the formula (19) by conventional methods to yield a compound of the formula (20), where R represents hydrogen or lower alkyl group,
(iv) benzylamino the compound of the formula (20) by conventional methods to yield a compound of the formula (10) where R has the meaning given above,
(v) hydrolysing the compound of the formula (10) by conventional methods followed by resolution to yield (S)-hydroxy compound of the formula (11),
(vi) converting the compound of the formula (11) to the corresponding alkylated compound of the formula (12) where R1 represents hydrogen or lower alkyl group, R2 represents lower alkyl group in one pot reaction by treating it with an alkylating agent in the presence of a base,
(vii) debenzylating the compound of the formula (12) by conventional methods to produce the compound of formula (13),
(viii) if desired, converting the compound of formula (13) to a compound of formula (14) where X represents halogen atom, R1 and R2 are as defined above, by conventional methods,
(ix) reacting either the compound of formula (13) or the compound of formula (14) with phenoxazinyl mesylate of the formula (15) to give the ester of the formula (16) where X represents hydrogen or halogen atom, R1 and R2 are as defined above,
(x) hydrolysing the compound of the formula (16) by conventional methods to yield the compound of the formula (1) defined above, and if desired,
(xi) chemically resolving the compound of formula (1) by employing chiral amines, in case there is any racemization during the course of converting the (S)-hydroxy compound of the formula (11) to the final compound of formula (1).
The process described above is as shown in scheme-4 below: 
Reaction of p-hydroxybenzaldehyde of the formula (7) with hydantoin of the formula (17) affords the unsaturated compound of the formula (18), which on hydrolysis gives the pyruvic acid derivative of the formula (19). The pyruvic acid derivative of the formula (19) is reduced in solvents such as methanol, ethanol, propanol, ethylacetate, and the like in the presence of Raney. Ni, H2/Pdxe2x80x94C to give the racemic hydroxy ester of the formula (20) (R represents hydrogen or lower alkyl group such as C1-C6 alkyl preferably methyl, ethyl and the like). The compound of formula (20) (where R represents hydrogen) has to be esterified using alcohol/sulphuric acid mixture to produce compound of formula (20) (where R represents lower alkyl group such as C1-C6 alkyl, preferably methyl, ethyl and the like). The alcohol used for esterification may be selected from methanol, ethanol and the like. The compound of formula (20) (where R represents lower alkyl group such as C1-C6 alkyl, preferably methyl, ethyl and the like) on selective benzylation of the phenolic group provides the compound of the formula (10). Hydrolysis of the compound of the formula (10) followed by its resolution using chiral amines such as R(+)-xcex1-methylbenzylamine, cinchonidine, ephedrine, S(+)phenylglycinol, n-octylglucosamine and the like gives the optically active hydroxy acid of the formula (11). Alkylation of the compound having the formula (11) using alkylating agents such as diethylsulphate, ethyliodide, methyliodide, dimethylsulhate and the like, in the presence of a base such as NaH, NaOH, KOH, t-BuOK, K2CO3, NaHCO3 and the like, affords the compound of the formula (12) where R1 represents hydrogen or lower alkyl group such as C1-C6 alkyl, preferably methyl, ethyl, propyl and the like, R2 represents lower alkyl group such as C1-C6 alkyl, preferably methyl, ethyl, propyl and the like. The compound of the formula (12) upon debenzylation using reagents such as H2/Pdxe2x80x94C, HCl/AcOH, and the like, in the presence of solvents such as THF, n-hexanol, n-octanol, 1,4-dioxane, AcOH and the like, gives the substituted phenol of the formula (13) defined earlier. The compound of the formula (13) is converted to a compound of formula (14) defined earlier using suitable halogenating agents such as ICl/HCl, I2/KI, Cl2/H+, Br/AcOH and the like. The optically active compound of the formula (13) or the compound of formula (14) reacts with the phenoxazinyl mesylate of the formula (15) to give the ester of the formula (16) which on hydrolysis employing conventional methods yields the required compound of the formula (1) in an optically pure form. However, in the event of a small amount of racemization, if any, during the course of converting the intermediate of the formula (11) to the final compound of the formula (1), resolution can easily be done employing chiral amines without loosing much of the compound of the formula (1).
The present invention also provides still another improved process for the preparation of compound of the formula (1) described above which comprises
(i) reacting p-hydroxybenzaldehyde of the formula (7) with hydantoin of the formula (17) by conventional methods to yield a compound of the formula (18),
(ii) hydrolysing the compound of the formula (18) by conventional methods to yield a compound of the formula (19),
(iii) reducing the compound of the formula (19) by conventional methods to yield a compound of the formula (20), where R represents hydrogen or lower alkyl group,
(iv) benzylamino the compound of the formula (20) by conventional methods to yield a compound of the formula (10) where R is as defined earlier,
(v) alkylating the compound of the formula (10) using alkylating agent in the presence of a base to obtain a compound of the formula (12a) where R1 represents hydrogen or lower alkyl group, R1 represents lower alkyl group,
(vii) debenzylating the compound of the formula (12a) by conventional methods to produce the compound of formula (13a) where R1 and R2 are as defined above, if desired,
(viii) converting the compound of formula (13a) to a compound of formula (14a) where X represents halogen atom, R1 and R2 are as defined above by conventional methods,
(viii) reacting either the compound of formula (13a) or the compound of formula (14a) with phenoxazinyl mesylate of the formula (15) to give the ester of the formula (4) where X represents hydrogen or halogen atom, R1 and R2 are as defined above,
(ix) hydrolysing the compound of the formula (4) by conventional methods to yield the racemic compound of the formula (5) where X represents hydrogen or halogen atom, R1 and R2 are as defined above, and
(x) chemically resolving the compound of formula (5) by employing chiral amines to the final compound of formula (1) optionally through an intermediate amide of the formula (6) where X represents hydrogen or halogen atom, and R1 and R2 are as defined above.
The process explained above is as shown in scheme-5 below: 
Reaction of p-hydroxybenzaldehyde of the formula (7) with hydantoin of the formula (17) affords the unsaturated compound of the formula (18), which on hydrolysis gives the pyruvic acid derivative of the formula (19). The pyruvic acid derivative of the formula (19) is reduced in solvents such as methanol, ethanol, propanol, ethylacetate, and the like, in the presence of Raney Ni, H2/Pdxe2x80x94C to give the racemic hydroxy ester of the formula (20) (R represents hydrogen or lower alkyl group such as C1-C6 alkyl, preferably methyl, ethyl and the like). The compound of formula (20) (where R represents hydrogen) has to be esterified using alcohol/sulphuric acid mixture to produce compound of formula (20) (where R represents lower alkyl group such as C1-C6 group; preferably methyl, ethyl and the like). The alcohol used for esterification may be selected from methanol, ethanol and the like. The compound of formula (20) (where R represents lower alkyl group such as C1-C6 group, preferably methyl, ethyl and the like) on selective benzylation of the phenolic group provides the compound of the formula (10), which on alkylation using alkylating agents such as diethylsuphate, ethyliodide, methyliodide, dimethylsulphate and the like, in the presence of a base such as NaH, NaOH, KOH, t-BuOK, K2CO3, NaHCO3, and the like, affords the compound of the formula (12a) where R1 represents hydrogen or lower alkyl group such as (C1-C6) alkyl, preferably methyl, ethyl, propyl and the like, R2 represents lower alkyl group such as (C1-C6) alkyl, preferably methyl, ethyl, propyl and the like. The compound of the formula (12a) upon debenzylation using reagents such as H2/Pdxe2x80x94C, HCl/AcOH, and the like in the presence of solvents such as THF, n-octanol, n-hexanol, 1,4-dioxane, AcOH and the like, gives the substituted phenol of the formula (13a). The compound of the formula (13a) is converted to a compound of formula (14a) using suitable halogenating agents such as ICl/HCl, I2/KI, Cl2/H+, Br2/AcOH and the like. The compound of the formula (13a) or the compound of formula (14a) reacts with the phenoxazinyl mesylate having the formula (15) to give the ester of the formula (4) which on hydrolysis employing conventional methods and resolution using chiral amines such as R(+)-xcex1-methylbenzylamine, S(+)-phenyl-glycinol, cinchoridine, ephedrine, n-octylglucosamine and the like yields the required compound of the formula (1) in an optically pure form.
The present invention further provides yet another improved process for the preparation of compounds of the formula (1) described above which comprises:
(i) selectively benzylamino L-tyrosine of the formula (21) by conventional methods to yield a compound of the formula (22),
(ii) diazotizing the compound of the formula (22) in the presence of an acidic reagent and an organic solvent to produce compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen or acetyl group),
(iii) if desired, hydrolysing the compound of formula (11xe2x80x2) (where Rxe2x80x2 represents acetyl group) to a compound of formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) by conventional methods,
(iv) converting the compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) to the alkyl compound of the formula (12) where R1 represents hydrogen or lower alkyl group, R2 represents lower alkyl group in one pot, by treating it with an alkylating agent in the presence of strong base,
(v) debenzylating the compound of the formula (12) by conventional methods to produce the compound of the formula (13) where R1 and R2 are as defined above, if desired,
(vi) converting the compound of formula (13) to a compound of formula (14) where X represents halogen, and R1 and R2 are as defined above, by conventional methods,
(vii) reacting either the compound of the formula (13) or the compound of formula (14) with phenoxazinyl mesylate of the formula (15) to give the ester of the formula (16) where X represents hydrogen or halogen atom, and R1 and R2 are as defined above,
(viii) hydrolysing the compound of the formula (16) by conventional methods to yield the compound of the formula (1) defined above, and if desired,
(ix) unresolved compound of formula (1) if any may be chemically resolved by employing chiral amines.
The process is shown in scheme-6 below: 
The process of the present invention starts from L-tyrosine of the formula (21) by selectively benzylamino it to afford the compound of the formula (22). Diazotisation of the compound of the formula (22) under acidic conditions using acids such as sulfuric acid, HCl, acetic acid and the like in appropriate organic solvent such as CHCl3, 1,4-dioxane, THF, acetone, and the like gives the compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen or acetyl group) in more than 98% ee (enantiomeric excess). Hydrolysis of the compound of formula (11xe2x80x2) (where Rxe2x80x2 represents acetyl group) to a compound of formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) may be carried out using conventional hydrolysing agents such as NaOH, KOH, LiOH, Ba(OH)2, and the like. Conversion of the compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) to the alkylated compound of the formula (12) where R1 represents hydrogen or lower alkyl group such as (C1-C6) alkyl preferably methyl, ethyl, propyl and the like, R2 represents lower alkyl group such as (C1-C6) alkyl preferably methyl, ethyl, propyl and the like, in one pot is achieved using alkylating agents such as diethylsulphate, ethyliodide, methyliodide, dimethyl-sulphate and the like in the presence of a strong base such as NaH, NaOH, KOH, t-BuOK, K2CO3, NaHCO3, and the like. Debenzylation of the compound of the formula (12) by conventional methods with H2/Pdxe2x80x94C, HCl/AcOH, and the like, in the presence of solvents such as THF, n-hexanol, n-octanol, 1,4-dioxane, AcOH and the like, afforded the required crucial intermediate compound of the formula (13) in very good yield (95%) and purity (95%). The compound of formula (13) is converted to a compound of formula (14) using suitable halogenating agents such as ICl/HCl, I2/KI, Cl2/H+, Br2/AcOH and the like. The optically active compound of the formula (13) or the compound of formula (14) is reacted with the phenoxazinyl mesylate having the formula (15) to give the ester of the formula (16) which on hydrolysis employing conventional methods yields the required compound of the formula (1) in an optically pure form and yield of 95%. However, in the event of a small amount of racemization, if any, resolution can easily be done employing chiral amines such as R(+)xcex1-methylbenzyl-amine, S(+)-phenylglycinol, cinchonidine, ephedrine, n-octyl-glucosamine and the like.
The present invention also provides an improved process for the preparation of compound of formula (13) where R1 represents hydrogen or lower alkyl group and R2 represents lower alkyl group which comprises:
(i) selectively benzylamino L-tyrosine of the formula (21) by conventional method to yield a compound of the formula (22),
(ii) diazotizing the compound of the formula (22) in the presence of an acidic reagent and an organic solvent to produce compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen or acetyl group), if desired,
(iii) hydrolysing the compound of formula (11xe2x80x2) (where Rxe2x80x2 represents acetyl group) to a compound of formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) by conventional methods,
(iv) converting the compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) to the compound of the formula (12) where R1 represents hydrogen or lower alkyl group, R2 represents lower alkyl group in one pot by treating it with an alkylating agent in the presence of strong base, and
(v) debenzylating the compound of the formula (12) by conventional methods to produce the compound of the formula (13) where R1 and R2 are as defined above.
The process is shown in scheme-7 below: 
The process of the present invention starts from L-tyrosine of the formula (21) by selectively benzylamino it to afford the compound of the formula (22). Diazotization of the compound of the formula (22) under acidic conditions acids using an acid such as sulfuric acid, HCl, acetic acid and the like in appropriate organic solvent such as CHCl3, 1,4-dioxane, THF, acetone, and the like gives the compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen or acetyl group) in more en 98% ee (enantiomeric excess). Hydrolysis of the compound of formula (11xe2x80x2) (where Rxe2x80x2 represents acetyl group) to a compound of formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) may be carried out using conventional hydrolysing agents such as NaOH, KOH, LiOH, Ba(OH)2, and the like. Conversion of the compound of the formula (11xe2x80x2) (where Rxe2x80x2 represents hydrogen) to the alkylated compound of the formula (12) where R1 represents hydrogen or lower alkyl group such as (C1-C6) alkyl, preferably methyl, ethyl, propyl and the like, R2 represents lower alkyl group such as (C1-C6) alkyl, preferably methyl, ethyl, propyl and the like, in one pot is achieved using alkylating agents such as diethyl sulphate, ethyl iodide, and the like in the presence of a strong base such as NaH, NaOH, KOH, t-BuOK, and the like. Debenzylation of the compound of the formula (12) by conventional methods with H2/Pdxe2x80x94C, HCl/AcOH, and the like, in the presence of solvents such as THF, n-hexanol, n-octanol, 1,4-dioxane, AcOH and the like, afforded the required of the formula (13) in very good yield (95% ) and purity (95%).
The present invention is described in detail with examples given below which are provided by way of illustration only and therefore should not be construed to limit the scope of the invention.